Albumin Labeled with Gd-DTPA: An Intravascular Contrast-Enhancing Agent for Magnetic Resonance Blood Pool Imaging: Preparation and Characterization

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A paramagnetic-labeled macromolecule, albumin-(Gd-DTPA), was prepared for use as an intravascular contrast agent for magnetic resonance imaging. An average of 19 Gd-DTPA chelates were covalently conjugated to human serum albumin through the bifunctional anhydride of DTPA. The albumin-(Gd-DTPA) was characterized with use of high-performance liquid chromatography, sodium dodecyl sulfate gel electrophoresis, atomic absorption, biuret and Bradford protein tests, and by its effect on proton relaxation (relaxivity). The average molecular weight was 92,000 daltons, indicating the albumin conjugate was predominantly monomeric. The T1 relaxivity of albumin-(Gd-DTPA) was 273mM-1sec-1 relative to carrier concentration, which corresponds to a relaxivity of 14.9mM-1sec-1 relative to gadolinium concentration. The average conditional stability constant for albumin-bound Gd-DTPA chelate was log K = 20.0. Spin-echo images of rats demonstrated persistent enhancement of vascular tissues and slowly flowing blood. Application of albumin-(Gd-DTPA) may augment the MR assessments of blood volume, tissue perfusion, and flow characteristics.

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